4 research outputs found
Insight into a Bentonite-Based Hydrogel for the Conservation of Sandstone-Based Cultural Heritage: In Situ Formation, Reinforcement Mechanism, and High-Durability Evaluation
Conservation of sandstone-based cultural heritage has
attracted
a great deal of interest. We propose herein a novel protecting strategy,
via in situ fabrication of bentonite-based hydrogels (B-H) inside
sandstones, where the bentonite-based hydrogels serve as the underlying
cement. To create bentonite-based hydrogels with controllable structure,
possessing good mechanical and anti-swelling properties, we have optimized
forming time, appearance, and viscosity. The hydrogel precursor penetrated
into the pores of the sandstone; the hydrogel would then form within
3–5 h. As found by employing a fluorescent tracer, the precursor
remained controllably in place without any apparent change in the
sandstone morphology. The bentonite-based hydrogels that formed inside
the sandstones presented strong hydrogen bonding, coordination, and
ionic bonding, as well as strong mechanical interlocking to the sandstone
matrix. As a result, the sandstones possessed enhanced mechanical
compressive strength and excellent resistance to acid, salt, and freeze–thaw
cycles. Our approach provides for a non-destructive, eco-friendly,
easy-to-use, and long-term strategy for cultural preservation, one
with excellent protection effects
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Insight into the Ligand-Mediated Synthesis of Colloidal CsPbBr<sub>3</sub> Perovskite Nanocrystals: The Role of Organic Acid, Base, and Cesium Precursors
While
convenient solution-based procedures have been realized for
the synthesis of colloidal perovskite nanocrystals, the impact of
surfactant ligands on the shape, size, and surface properties still
remains poorly understood, which calls for a more detailed structure–morphology
study. Herein we have systematically varied the hydrocarbon chain
composition of carboxylic acids and amines to investigate the surface
chemistry and the independent impact of acid and amine on the size
and shape of perovskite nanocrystals. Solution phase studies on purified
nanocrystal samples by <sup>1</sup>H NMR and IR spectroscopies have
confirmed the presence of both carboxylate and alkylammonium ligands
on surfaces, with the alkylammonium ligand being much more mobile
and susceptible to detachment from the nanocrystal surfaces during
polar solvent washes. Moreover, the chain length variation of carboxylic
acids and amines, ranging from 18 carbons down to two carbons, has
shown independent correlation to the size and shape of nanocrystals
in addition to the temperature effect. We have additionally demonstrated
that employing a more soluble cesium acetate precursor in place of
the universally used Cs<sub>2</sub>CO<sub>3</sub> results in enhanced
processability without sacrificing optical properties, thus offering
a more versatile recipe for perovskite nanocrystal synthesis that
allows the use of organic acids and amines bearing chains shorter
than eight carbon atoms. Overall our studies have shed light on the
influence of ligand chemistry on crystal growth and stabilization
of the nanocrystals, which opens the door to functionalizable perovskite
nanocrsytals through surface ligand manipulation
Nanorod Suprastructures from a Ternary Graphene Oxide–Polymer–CsPbX<sub>3</sub> Perovskite Nanocrystal Composite That Display High Environmental Stability
Despite
the exceptional optoelectronic characteristics of the emergent
perovskite nanocrystals, the ionic nature greatly limits their stability,
and thus restricts their potential applications. Here we have adapted
a self-assembly strategy to access a rarely reported nanorod suprastructure
that provide excellent encapsulation of perovskite nanocrystals by
polymer-grafted graphene oxide layers. Polyacrylic acid-grafted graphene
oxide (GO-<i>g</i>-PAA) was used as a surface ligand during
the synthesis of the CsPbX<sub>3</sub> perovskite nanocrystals (NCs),
yielding particles (5–12 nm) with tunable halide compositions
that were homogeneously embedded in the GO-<i>g</i>-PAA
matrix. The resulting NC-GO-<i>g</i>-PAA exhibits a higher
photoluminescence quantum yield than previously reported encapsulated
NCs while maintaining an easily tunable bandgap, allowing for emission
spanning the visible spectrum. The NC-GO-<i>g</i>-PAA hybrid
further self-assembles into well-defined nanorods upon solvent treatment.
The resulting nanorod morphology imparts extraordinary chemical stability
toward protic solvents such as methanol and water and much enhanced
thermal stability. The introduction of barrier layers by embedding
the perovskite NCs in the GO-<i>g</i>-PAA matrix, together
with its unique assembly into nanorods, provides a novel strategy
to afford robust perovskite emissive materials with environmental
stability that may meet or exceed the requirement for optoelectronic
applications
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General Strategy for the Preparation of Stable Luminous Nanocomposite Inks Using Chemically Addressable CsPbX<sub>3</sub> Peroskite Nanocrystals
The potential optoelectronic
applications of perovskite nanocrystals
(NCs) are primarily limited by major material instability arising
from the ionic nature of the NC lattice. Herein, we introduce a facile
and effective strategy to prepare extremely stable CsPbX<sub>3</sub> NC–polymer composites. NC surfaces are passivated with reactive
methacrylic acid (MA) ligands, resulting in the formation of homogeneous
nanocubes (abbreviated as MA-NCs) with a size of 14–17 nm and
a photoluminescence quantum yield above 80%. The free double bonds
on the surface then serve as chemically addressable synthetic handles,
enabling UV-induced radical polymerization. Critically, a bromide-rich
environment is developed to prevent NC sintering. The composites obtained
from copolymerizing MA-NCs with hydrophobic methyl methacrylate and
methacrylisobutyl polyhedral oligomeric silsesquioxane monomers exhibit
enhanced properties compared to previously reported encapsulated NCs,
including higher quantum yields, remarkable chemical stability toward
water, and much enhanced thermal stability. The good solubility of
the composite in organic solvent further enables its use as a solution-processable
luminescent ink, used here for fabrication of white-light-emitting
diodes with high luminous efficiency and excellent color-rendering
index. The resulting fluorescent and stable NC ink opens the door
to potential scalable and robust optoelectronic applications